Jenkins连接FTP失败

问题遇到的现象和发生背景
想用Jenkins连接FTP，一直连接不上，不知道原因，报错如下

运行结果及报错内容
jenkins.plugins.publish_over.BapPublisherException: Failed to connect and initialize FTP connection. Message: [org.apache.commons.net.ftp.FTPConnectionClosedException: FTP response 421 received. Server closed connection.]